An 8-month-old boy who, investigators say, was seriously injured at the hands of his mother who is also facing murder charges in the deaths of his two siblings, has died, the Plymouth County District Attorney's Office said. Subscribe to WCVB on YouTube now for more: http://bit.ly/1e8lAMZ Get more Boston news: http://www.wcvb.com Like us: https://www.facebook.com/wcvb5 Follow us: https://twitter.com/WCVB Instagram: https://www.instagram.com/wcvb5/